The present invention relates to a sliding member, such as a piston ring for use in internal combustion engines, having an ion-plating deposition layer, or film, of chrome nitride formed on the sliding surface thereof.
For a sliding member, such as a piston ring for use in internal combustion engines, a technique of enhancing the abrasion resistance thereof has been made public in Japanese Patent Laid-Open Publication (JP-A) 8-296030 (1996), where the enhancement is enabled by forming an ion-plating deposition layer of CrN, also including Cr2N, on the external circumferential sliding surface thereof, by means of a physical vapor deposition (PVD) method.
There are two types in the publicly known ion-plating deposition layers composed mainly of chrome nitride including Cr2N and CrN, i.e., one type of deposition layer having the CrN of the chrome nitride which has a preferred orientation of the plane {111}, and the other type having the CrN of the chrome nitride which has a preferred orientation of the plane {100}. A deposition layer of the CrN having the preferred orientation of the plane {111}, is superior in abrasion resistance and scuffing resistance, but, due to having high internal stress, is inferior in peeling resistance, to a deposition layer of CrN having the preferred orientation of the plane {100}. On the contrary, or inversely, a deposition layer of the CrN having the preferred orientation of the plane {100}, is inferior in abrasion resistance and scuffing resistance, but, because of the porosity thereof being easily controllable, is superior in peeling resistance, to a deposition layer of the CrN having the preferred orientation of the plane {111}.
An object of the present invention therefore is to provide a sliding member having an ion-plating deposition layer, composed mainly of chrome nitride including Cr2N and CrN, that has peeling resistance enhanced, or improved, while maintaining the excellent abrasion and scuffing resistance level of a deposition layer of the CrN which has a preferred orientation of the plane {111}.
According to an embodiment of the present invention, an improved sliding member is provided that has a sliding surface and a deposition layer formed on the sliding surface by means of an ion-plating method, wherein the deposition layer is composed mainly of chrome nitride, including CrN. The improvement comprises the CrN of the chrome nitride which has a preferred orientation plane of {111}, where the deposition layer contains boron in an amount of not less than 0.05 and not more than 20 weight percent.
According to another embodiment of the present invention, an improved sliding member is provided which has a sliding surface and a deposition layer formed on the sliding surface by means of an ion-plating method, wherein the deposition layer is composed mainly of chrome nitride, including CrN. The improvement includes the CrN of the chrome nitride having a preferred orientation plane of {111}, where the deposition layer contains boron in an amount of not less than 0.05 and not more than 20 weight percent, and either one or both of oxygen and carbon in an amount of not more than 15 weight percent.
With an improved sliding member obtained by the use of the deposition layer as described above, according to the present invention, enhanced peeling resistance is obtained which is better than that of the conventional sliding members having an ion-plating deposition layer which does not contain boron, with the CrN having the preferred orientation plane of {111}, while maintaining the excellent abrasion resistance and scuffing resistance of the conventional sliding members having an ion-plating deposition layer which does not contain boron, with the CrN having the preferred orientation of the plane {111}.
The reason that abrasion resistance and scuffing resistance of the deposition layer are enhanced by adding boron, may be described in that, boron is considered to have a higher free composing energy in chrome than other elements, such as carbon, oxygen and nitrogen, have in chrome. Therefore boron does not tend to form a boride, and does tend to form a solid solution either in chrome or chrome nitride of CrxN, thereby producing a greater effect on strengthening the base of the deposition layer, resulting in enhanced abrasion resistance and scuffing resistance.